This invention relates to apparatus for producing fiberboard for manufacture according to the dry method in which a a continuous sheet is formed from cellulosic fibers or shavings and thereupon compacted and subdivided into board units which are subjected to a pressure and heat treatment.
In manufacture of sheet or board units or similar products by known methods and apparatus as referred to herein, air is evacuated from the continuous fiber sheeting during a compression step immediately following the forming step. The compression is effectuated by various types of belt or strap presses and the air is evacuated by being forced out of the fiber sheeting laterally in the belt or strap press.
The resultant high velocity air flow transversely to the direction of a movement of the sheeting disturbs the orientation of the fibers in the fiber sheeting. As the fiber sheeting before it is compressed and has acquired sufficient stability must be carried by a wire cloth or similar support means the latter means must also be passed through the belt press with consequent risk of damage that may be caused by the high linear pressure and point pressure exerted by the press.
In the method of producing of sheet and board units described above it is also of greatest importance to maintain a high speed rate of feed in order to produce the greatest possible number of board units per unit of time. In the known methods and apparatuses referred to above for compressing and evacuating air from the continuous fiber sheeting directly after the forming step when high a rate of feed speed is required, the air removal from the fiber sheeting constitutes a capacity limiting factor unless the air can be evacuated at a sufficiently rapid pace.